The HIV pandemic and its burden on women highlights the urgent need for effective pre-exposure prophylaxis (PrEP). We hypothesize that the optimal strategy will require combining potent antiretroviral (ARV) drugs that are active in multiple compartments (vaginal, cervical, and rectal), exhibit rapid and sustained pharmacokinetics (PK), are effective against multiple clades, and are safe. Ideally, sustained delivery formulations should be prioritized, as adherence to daily or coitally dependent dosing has proven difficult. Building from these concepts, this Integrated Preclinical/Clinical Program will focus on intravaginal ring (IVR) delivery of tenofovir disoproxil fumarate (TDF), the more potent prodrug of tenofovir (TFV), in combination with maraviroc, an entry inhibitor, or with IQP-0528, a non-nucleoside reverse transcriptase and entry inhibitor that we have successfully formulated for IVR delivery. We will also study GS7340, a newer TFV prodrug in development, with potentially better distribution into lymphoid tissues. The conflicting results of recent topical and oral PrEP trials highlight the complexities in translating preclinical data into real world use. The variable clinical outcomes may reflect differences in dosing (coitally dependent vs. daily) or in adherence. However, other important biological factors, including age, hormonal contraception, semen and vaginal microbiota may have acted on the genital mucosal environment to alter drug PK, antiviral activity (pharmacodynamics (PD)), and susceptibility to HIV, shifting the balance between protection and infection. To address this critical knowledge gap, we propose intensive PK/PD studies in non-human primates (Project 1) and exploratory clinical studies in well-characterized cohorts of U.S. and sub-Saharan African women to assess how clinical variables modulate drug PK/PD using novel ex vivo cell and tissue culture models (Projects 2 and 3), supported by a bioanalytical scientific core. Our goal is to optimize sustained IVR delivery of an ARV combination that will provide protective drug levels at the sites of HIV infection in high risk women. We will test a PK/PD model in a pre-Phase I TDF IVR study in women at risk for HIV acquisition. Results obtained will enable us to optimize IVR combinations for future clinical studies.